GIFT   OF 


NEW   MAMMALIAN   FAUNAS   FROM   MIOCENE 

SEDIMENTS  NEAR  TEHACHAPI  PASS  IN 

THE  SOUTHERN  SIERRA  NEVADA 


A  THESIS  SUBMITTED  IN  PARTIAL  SATISFACTION  OF 
THE  REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 
AT  THE  UNIVERSITY  OF  CALIFORNIA 


JOHN  PETER  BUWALDA 


MAY,  1915 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

BULLETIN   OF  THE   DEPARTMENT  OF 

GEOLOGY 

Vol.  10,  No.  6,  pp.  75-85  Issued  November  18,  1916 


NEW   MAMMALIAN   FAUNAS   FROM  MIOCENE 

SEDIMENTS  NEAR  TEHACHAPI  PASS  IN 

THE  SOUTHERN  SIERRA  NEVADA 


BY 

JOHN  P.  BUWALDA 


CONTENTS 

PAGE 

Introduction 75 

Occurrence  76 

Phillips  Eanch  Fauna 77 

Cache  Peak  Fauna 80 

Kelationships  of  the  Faunas  

Geologic  Significance  of  the  Faunas  

INTRODUCTION 

During  the  past  five  years  expeditions  under  the  direction  of  the 
Department  of  Palaeontology  of  the  University  of  California  have 
made  considerable  collections  of  Tertiary  mammalian  fossils  in  for- 
mations near  Barstow  and  at  Eicardo,  in  the  Mojave  Desert.  Mam- 
malian material  has  also  been  obtained  in  sections  containing  marine 
formations  in  the  Southern  San  Joaquin  Valley,  on  the  western  or 
opposite  side  of  the  southern  Sierra  Nevada.  Study  of  this  material 
from  the  Mojave  Desert  and  the  San  Joaquin  Valley  has  yielded 
important  information  regarding  the  history  of  mammalian  life  in 
these  regions.  With  the  geologic  data  obtained  it  is  being  made  the 
basis  for  a  beginning  in  the  correlation  of  events  in  the  Tertiary 
palaeontologic  and  geologic  history  of  the  Great  Basin  and  Pacific 
Coast  provinces. 

With  a  view  to  contributing  to  the  solution  of  this  general  problem 
of  Cenozoic  correlation  between  the  Great  Basin  and  Pacific  Coast 


319566 


76  University  of  California  Publications  in  Geology        [VOL.  10 

provinces,  the  writer  examined  an  area  of  sedimentary  deposits  near 
Tehachapi  Pass,  in  the  southern  Sierra  Nevada.  This  area  lies  directly 
between  the  San  Joaquin  Valley  and  the  Mojave  Desert.  Because  of 
its  position  it  seemed  probable  that  its  study  would  yield  critical  infor- 
mation bearing  upon  the  question  of  correlation  between  the  two 
provinces.  Reconnaissance  examinations  by  the  writer  in  the  winter 
of  1912  and  in  the  summer  of  1914  had,  moreover,  suggested  the  proba- 
bility of  the  presence  of  mammalian  fossils  in  the  exposures  of  sedi- 
mentary strata  in  the  Tehachapi  area. 

As  the  result  of  several  weeks'  work  in  the  Tehachapi  Pass  region 
in  November  and  December,  1914,  two  fossil  faunas  were  secured  at 
quite  widely  separated  horizons.  More  material  was  obtained  in  June, 
1915,  in  the  collection  of  which  the  writer  was  ably  assisted  by  Clarence 
L.  Moody,  James  M.  Douglas,  and  Edward  Thacher. 

Though  the  collections  are  not  large,  they  are  thought  to  contribute 
new  information  relating  to  the  history  of  the  Mammalia  of  western 
North  America,  and  bearing  on  the  geologic  history  of  the  southern 
Sierra  Nevada  and  adjacent  regions. 

This  paper  is  a  summary  statement  of  the  composition  and  rela- 
tionships of  these  faunas.  Detailed  descriptions  of  the  faunas  and  a 
discussion  of  the  geologic  results  are  to  follow. 

OCCURRENCE 

The  Tertiary  formations  in  which  the  mammalian  faunas  are  found 
in  the  Tehachapi  region  are  in  part  an  extension  of  beds  first  brought 
to  notice  by  Professor  Andrew  C.  Lawson,1  who  described  strata  ex- 
posed in  the  vicinity  of  Monolith  and  lower  Cache  Creek,  near  Teha- 
chapi Pass. 

The  formations  are  included  in  a  section  of  volcanic  and  terrestrial 
materials  extending  over  an  area  of  seventy-five  to  eighty  square  miles 
or  more  of  the  summit  region  of  the  southern  Sierra  northeast  of  the 
town  of  Tehachapi.  The  total  thickness  of  the  formations  is  probably 
not  less  than  four  or  five  thousand  feet.  Constituting  the  group  are 
basic  lava  flows,  volcanic  agglomerates,  massive  pumiceous  tuffs,  strati- 
fied ash  beds,  terrestrial  sandstones,  clays,  cherts,  and  fanglomerates. 
The  fossiliferous  horizons  are  probably  stratigraphically  near  the 
middle  of  the  section.  The  whole  succession  of  strata  records  recur- 
rent volcanic  activity,  with  intervening  periods  of  subaerial  and  lacus- 
tral  deposition.  The  angular  fanglomeratic  character  of  the  coarser 


Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  4,  pp.  431-462,  1906. 


1916]   Buwalda:  Miocene  Mammalian  Faunas  from  Tehachapi  Pass     77 

sediments  and  the  similarity  of  the  finer  beds  to  playa  lake  deposits 
strongly  suggest  that  the  climate  was  arid  or  semi-arid,  rather  than 
humid.  The  presence  of  palm  leaves  near  the  lower  of  the  horizons 
at  which  mammalian  remains  were  found  does  not  conflict  with  this 
inference. 

Since  their  deposition  the  series  of  deposits  containing  the  faunas 
have  been  folded,  with  dips  up  to  30  degrees.  The  tilted  strata  have 
been  in  part  cut  away  by  erosion,  and  their  deep  dissection  has  afforded 
excellent  opportunity  for  securing  collections  of  the  contained  fossil 
remains.  The  fossils  were  obtained  from  badland  surfaces,  on  which 
they  lie  where  the  matrix  has  been  blown  or  washed  away,  and  from 
rocky  shelves  on  the  bluffs  in  which  the  fossils  were  embedded. 

The  two  localities  from  which  the  faunas  were  collected  are  situ- 
ated about  three  miles  apart.  The  lower  fauna  was  found  in  sand- 
stones, containing  chert  layers,  about  nine  miles  northeast  of  the  town 
of  Tehachapi,  and  one  mile  northeast  of  Phillips  Ranch,  which  is  on 
Sand  Creek,  a  tributary  of  Cache  Creek.  This  assemblage  may  be 
known  as  the  Phillips  Ranch  fauna.  The  second  or  younger  fauna 
occurs  in  coarse  sandstones  and  fine  fanglomerates  exposed  along  the 
south  fork  of  upper  Cache  Creek,  about  three  and  one-half  miles  east 
of  Phillips  Ranch.  This  upper  mammal-bearing  horizon  passes  under 
Cache  Peak  on  the  divide  between  Cache  Creek  and  Jawbone  Canon. 
This  will  be  known  as  the  Cache  Peak  fauna.  Strata  of  an  estimated 
thickness  of  five  hundred  feet  separate  the  horizons  of  the  Phillips 
Ranch  and  Cache  Peak  faunas.  It  is  quite  possible  that  an  uncon- 
formity occurs  in  the  section  between  the  two  faunas;  evidence  sug- 
gesting an  erosion  interval  was  noted  in  upper  Oil  Canyon,  a  tributary 
of  Cache  Creek  from  the  south. 

The  Phillips  Ranch  fauna  was  obtained  at  a  single  locality  ex- 
tending only  a  few  hundred  feet  along  the  outcrop  of  the  beds  and 
through  but  fifty  or  seventy-five  feet  of  the  strata.  The  Cache  Peak 
material  was  collected  from  exposures  distributed  over  an  area  perhaps 
two  miles  long  and  extending  through  several  hundred  feet  of  beds. 

PHILLIPS  RANCH  FAUNA 

The  collection  from  the  lower  horizon  near  Phillips  Ranch  includes 
the  following  forms : 

Merychippus,  n.  sp.  Merycodus?  sp. 

Camelid,  large  Carnivore,  indet. 

Camelid,  small  Canid,  indet. 

Moropus,  sp.  Felid,  indet. 


78  .   University  of  California  Publications  in  Geology        [V°L-  10 

The  horses  of  the  Phillips  Ranch  fauna  are  of  a  type  in  or  near 
the  genus  Merychippus,  but  possibly  represent  a  new  subgenus  of 
that  group  less  advanced  in  tooth  structure  than  typical  Merychippus. 
They  are  represented  by  upper  and  lower  cheek-teeth  and  by  a  number 
of  limb  bones.  The  upper  cheek-teeth  are  short  hypsodont,  the  height 
being  about  equal  to  or  a  little  greater  than  the  transverse  diameter 
in  well  worn  teeth.  The  teeth  are  small,  those  in  the  middle  of  the 
series  ranging  from  15.6  to  17.1  mm.  in  anteroposterior  diameter  and 
from  about  15  to  16.4  mm.  transverse  diameter.  Height  of  worn  teeth 
On  the  outer  side  is  15  to  18  mm.,  on  inner  side  10.2  to  12.2  m.  They 
are  relatively  narrow  transversely  compared  with  the  teeth  of  typical 
species  of  Merychippus.  The  outer  and  inner  faces  are  not  approxi- 
mately parallel  as  in  strictly  prismatic  teeth,  but  approach  each  other 
somewhat  toward  the  summits  of  the  teeth.  The  crowns  are  slightly 
curved.  They  are  well  cemented,  but  the  cement  covering  is  not  heavy. 
The  outer  faces  of  paracone  and  metacone  are  flat  or  have  a  very  faint 
median  rib.  The  mesostyle  is  prominent,  narrow,  and  may  be  of  nearly 
equal  width  from  base  to  summit  of  tooth,  or  may  flare  slightly  at  the 
base.  The  protoconule  and  metaconule  are  slightly  larger  than  proto- 
cone  and  hypocone.  The  protoconule  is  slightly  crescentic  and  is 
broadly  connected  with  the  oval  protocone.  The  metaloph  is  com- 
pletely connected  with  ectoloph,  but  is  usually  not  connected  with 
protoloph  because  of  imperfect  development  of  the  posterior  horn  of 
the  protoconule.  The  fossettes  are  well  cemented,  with  one  or  two 
crinkles  in  the  enamel  borders.  The  prefossette  is  usually  open  on  the 
median  or  inner  border  between  protoloph  and  metaloph.  The  post- 
fossette  is  sometimes  closed  and  sometimes  open  between  hypocone 
and  hypostyle. 

The  upper  cheek-teeth  are  more  advanced  than  those  of  Parahippus 
and  the  other  genera  of  the  Anchitheriinae  in  the  greater  height  of 
the  crowns  and  in  their  prismatic  form,  in  their  strong  cementation, 
in  the  relatively  large  size  of  protoconule  and  metaconule  compared 
with  protocone  and  hypocone,  and  in  the  tendency  to  close  the  fos- 
settes. They  are  relatively  primitive  compared  with  described  forms 
of  Merychippus  in  their  small  size,  shorter  crowns,  subequality  in  size 
of  protocone  and  protoconule,  in  the  imperfect  development  of  the 
posterior  horn  of  the  protoconule,  and  in  the  general  openness  of  the 
fossettes  on  the  inner  side. 

The  characters  are  in  a  measure  those  assigned  by  Gidley2  to 
hypothetical  genera  of  a  group  "C"  of  division  "Anchitheriinae 


2  Gidley,  J.  W.,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  23,  p.  868,  1907. 


1916]   Buwalda:  Miocene  Mammalian  Faunas  from  Tehachapi  Pass     79 

Leidy":  "Inner  conules  (pr  and  hy)  smaller  than  median  conules 
(pi  and  ml),  protoconule  semi-crescentic ;  partially  or  completely 
united  with  the  metaloph.;  ..." 

The  lower  cheek-teeth  of  this  equid  form  are  all  of  one  type,  char- 
acterized by  being  distinctly  hypsodont,  and  well  cemented.  Their 
length  is  approximately  one  to  one  and  one-half  times  their  antero- 
posterior  diameter.  The  metaconid-metastylid  column  is  well  devel- 
oped. The  marked  groove  between  the  metaconid  and  metastylid  per- 
sists nearly  to  the  base  of  the  tooth.  The  lower  cheek-teeth  seem  in 
some  respects  more  advanced  than  the  upper,  but  certainly  represent 
the  same  form,  as  the  upper  and  lower  teeth  of  the  same  individual 
have  been  found  together. 

In  one  specimen  (no.  21692)  lower  milk  teeth  are  present  in  the 
jaw  with  the  permanent  teeth.  The  deciduous  teeth  are  of  the  short- 
crowned  type  and  bear  a  thin  cement  layer. 

With  the  horse  teeth  are  three  astragali  and  scattered  litnb  bones 
representing  small  forms.  One  of  the  three  astragali  is  much  smaller 
than  the  others  and  possibly  represents  a  type  distinct  from  that 
indicated  by  the  other  material. 

The  camels  of  the  Phillips  Ranch  fauna  are  known  from  cheek- 
teeth, an  astragalus,  a  distal  portion  of  a  radius,  a  distal  portion  of  a 
tibia,  and  by  a  number  of  foot  bones.  The  material  probably  does  not 
permit  of  specific  determination,  but  difference  in  the  size  of  the  teeth 
suggests  that  a  large  and  a  small  species  of  camel  are  present. 

Moropus  is  indicated  in  the  assemblage  of  species  by  a  portion  of 
a  lower  jaw  containing  three  premolars  and  a  molar,  all  little  worn. 
Compared  with  Moropus  elatus  Marsh,  the  teeth  in  this  jaw  are  con- 
siderably smaller  and  are  relatively  narrower  transversely. 

An  incomplete  calcaneum  closely  resembles  that  of  the  antelope- 
like  Merycodus. 

A  toothless  carnivore  jaw  represents  a  small  form  which  is  probably 
not  generically  determinable. 

A  part  of  a  lower  jaw,  probably  of  a  canid,  and  a  portion  of  a  tooth, 
apparently  a  felid,  likewise  do  not  admit  of  exact  identification. 

The  evidence  as  to  age  of  the  Phillips  Ranch  fauna  is  furnished 
principally  by  the  horse  material.  The  Merychippus  is  possibly  so 
primitive  that  it  should  be  set  off  as  a  new  subgenus.  Merychippus 
is  usually  held  to  range  from  middle  Miocene  to  early  Pliocene.  It 
appears  that  this  faunal  stage  is  not  younger  than  middle  Miocene  and 
may  represent  a  somewhat  earlier  stage  of  that  period. 


80  University  of  California  Publications  in  Geology        [VOL.  10 

CACHE  PEAK  FAUNA 

The  Cache  Peak  fauna  includes  the  following  forms : 

Merychippus,  n.  sp.,  a  Merycochoerus(?),  sp. 

Merychippus,  n.  sp.,  b  Dromomeryx,  sp. 

Hypohippus,  sp.  Merycodus,  sp. 

Camelid,  sp.,  a  Felid,  sp. 
Camelid,  sp.,  b 

Of  the  three  forms  of  horses  only  one  is  represented  by  sufficient 
material  to  make  possible  a  full  study.  Of  this  type  there  were  ob- 
tained a  nearly  complete  skull  (no.  22254,  Univ.  Calif.  Loc.  2735)  with 
complete  upper  cheek  dentition,  a  complete  femur,  complete  meta- 
podial  region  with  lateral  elements  and  phalangeal  series,  and  the  ex- 
tremities of  a  number  of  other  limb  bones.  No  lower  teeth  of  this 
individual  were  found. 

The  notable  characters  of  the  dentition  of  this  specimen  are  as 
follows:  Upper  cheek-teeth  short  hypsodont  and  well  cemented. 
Mesostyle  strongly  developed.  Protocone  flat  oval  in  cross-section  and 
slightly  smaller  than  the  protoconule,  distinctly  connected  with  the 
protoconule  in  every  tooth  in  the  skull.  Protoconule  and  metaconule 
not  notably  crescentic.  Postfossette  closed  in  all  the  teeth ;  pref ossette 
closed  on  the  inner  or  median  side  in  seven  of  the  twelve  teeth. 

Several  other  upper  cheek-teeth  from  the  Cache  Peak  horizon,  some 
unworn,  are  of  the  same  type  as  those  of  no.  22254,  and  exhibit  no 
new  characters.  In  the  course  of  wear  the  protocone  of  these  teeth 
would  be  disconnected  from  the  protoconule  until  approximately  the 
upper  half  of  the  tooth  had  been  worn  away. 

Several  lower  cheek-teeth  in  the  collections,  presumably  represent- 
ing the  form  seen  in  no.  22254,  are  also  quite  heavily  cemented. 

The  type  of  horse  represented  by  these  upper  and  lower  cheek-teeth 
is  certainly  to  be  characterized  as  a  species  of  Merychippus  as  this 
group  is  at  present  defined,  and  is  not  one  of  the  most  primitive 
members  of  the  group. 

The  second  form  of  horse  in  the  Cache  Peak  fauna  is  known  only 
by  parts  of  three  upper  cheek-teeth,  two  of  which  fortunately  exhibit 
the  protocone-protoconule  relation.  These  teeth  are  badly  worn,  but 
the  crowns  appear  to  have  been  rather  short  hypsodont,  well  cemented, 
and  somewhat  curved.  The  most  notable  feature  is  the  fact  that  the 
protocone  as  shown  in  no.  21693  is  widely  disconnected  from  the  proto- 
conule to  the  very  base  of  the  tooth,  and  that  it  is  short  oval  in  cross- 
section.  The  protoconule  in  this  specimen  is  distinctly  larger  than 


1916]   Buwalda:  Miocene  Mammalian  Faunas  from  Tekachapi  Pass     81 

the  protocone,  is  markedly  crescentic  in  outline,  and  is  connected  with 
the  metaloph.  The  last  three  characters  are  among  those  which  set  off 
the  Merychippus  group  from  the  earlier  horses.  So  far  as  can  be 
judged  from  the  scanty  material,  this  form  should  be  included  within 
the  genus  Merychippus,  but  the  disconnected  protocone  indicates  that 
it  probably  lies  within  that  division  of  the  genus  leading  toward  the 
Hipparion  stock  rather  than  within  the  division  which  probably  gave 
rise  to  Protohippus,  Pliokippus,  and  other  forms  with  connected  pro- 
tocone. 

The  Hypohippus  material  consists  of  three  upper  cheek-teeth.  The 
advanced  state  of  wear  will  probably  not  permit  the  safe  reference  of 
the  form  represented  by  the  teeth  to  any  of  the  described  species  of 
Hypohippus. 

The  collection  from  the  Cache  Peak  horizon  includes  a  considerable 
amount  of  camel  material,  consisting  of  imperfect  limb  bones,  with  a 
few  parts  of  teeth.  The  remains  indicate  the  presence  of  at  least  two 
forms.  Fragmentary  teeth  and  some  of  the  limb  bones  represent  a 
species  near  Procamelus.  Certain  of  the  other  parts,  such  as  a  crushed 
proximal  extremity  of  a  metapodial  and  two  imperfect  astragali,  repre- 
sent a  camel  decidedly  larger  than  the  first  species  mentioned. 

Of  the  two  teeth  indicating  the  presence  of  an  oreodont  in  the 
fauna  one  is  presumably  Merycochoerus;  the  other  may  be  generically 
distinct. 

The  antelope-like  Dromomeryx  is  represented  in  the  Cache  Peak 
fauna  by  two  lower  teeth.  While  it  is  not  desirable  to  attempt  a 
specific  determination  with  such  scanty  material,  the  characters  of  the 
genus  are  well  shown  in  the  accessory  median  tubercle,  the  accessory 
anterior  ridge  developed  from  the  cingulum,  and  in  the  roughened 
surface  of  the  enamel.  The  " Palaeomeryx  fold"  on  the  anterior  ex- 
ternal crescent  is  shown  on  one  of  the  teeth.  Dromomeryx  has  been 
reported  from  middle  Miocene  to  early  Pliocene. 

The  fragmentary  Merycodus  material  indicates  a  small  species  of 
that  genus.  This  form  may  be  the  same  as  that  occurring  in  the 
Barstow  fauna. 

A  felid  is  known  in  the  fauna  by  the  distal  portion  of  a  meta- 
carpal  or  metatarsal. 

EELATIONSHIPS  OF  THE  FAUNAS 

A  comparison  of  the  Phillips  Eanch  and  Cache  Peak  faunas  must 
at  present  be  based  largely  upon  the  horses  represented  in  the  two 


82  University  of  California  Publications  in  Geology        [VOL.  10 

collections.  Moropus  occurs  only  in  the  former  fauna,  while  Meryco- 
choerus(?)  and  Dromomeryx  are  found  only  in  the  latter,  but  the 
collections  are  not  sufficiently  large  to  make  the  absence  of  a  form 
from  one  fauna  and  its  presence  in  the  other  significant.  Merycodus 
is  present  in  the  collections  from  both  localities,  but  the  material  is  too 
scanty  to  allow  an  accurate  comparison. 

Of  the  horses,  the  species  from  the  Phillips  Ranch  horizon  has  much 
smaller  and  much  more  primitive  cheek-teeth  than  either  of  the  forms 
in  the  Cache  Peak  fauna.  The  horse  astragali  from  the  Phillips  Ranch 
horizon  are  all  of  a  smaller  type,  while  there  are  in  the  collections  from 
the  upper  horizon  astragali  of  a  larger  type  as  well. 

The  evidence  of  the  camel  material  is  not  emphatic,  but  the  larger 
size  of  most  of  the  camel  teeth  and  foot  parts  in  the  Cache  Peak  fauna 
tends  to  confirm  the  view  that  this  assemblage  represents  a  more 
advanced  stage. 

The  Phillips  Ranch  fauna  is  quite  certainly  considerably  older  and 
less  advanced  than  the  assemblage  from  the  Cache  Peak  horizon. 

In  considering  the  relations  of  the  Phillips  Ranch  and  Cache  Peak 
faunas  to  other  groups  it  seems  desirable  to  compare  them  with  faunas 
known  from  neighboring  areas.  In  the  Mojave  Desert  the  Ricardo 
fauna,  known  from  considerable  collections  to  be  of  approximately 
lower  Pliocene  age,  occurs  about  twenty  miles  to  the  northeast ;  the 
Barstow  fauna,  also  well  represented  by  material  and  of  approxi- 
mately upper  Miocene  age,  is  found  about  eighty  miles  to  the  east. 
In  the  southern  San  Joaquin  Valley  on  the  opposite  side  of  the  south- 
ern Sierra  a  meager  collection  obtained  in  the  Tejon  Hills  is  of  ap- 
proximately very  late  Miocene  or  lower  Pliocene  age. 

The  species  of  Meryckippus  found  in  the  Phillips  Ranch  fauna  is 
very  different  from  any  species  found  in  the  Barstow  upper  Miocene 
collection,  being  much  more  primitive.  The  camels  do  not  permit  of 
an  exact  comparison  because  of  scantiness  of  the  Phillips  Ranch 
material,  but  they  appear  to  be  different.  The  species  of  Merycodus 
may  be  the  same  as  that  from  Barstow,  but  with  the  material  at  hand 
a  certain  determination  cannot  be  made. 

The  horse  material  from  Phillips  Ranch  resembles  still  less  any  of 
the  horses  found  in  the  Ricardo  fauna,  being  much  more  primitive. 
It  is  likewise  less  advanced  than  the  horse  species  obtained  in  the 
Tejon  Hills  in  the  southern  San  Joaquin  Valley. 

The  Phillips  Ranch  fauna  certainly  represents  a  stage  of  evolu- 
tionary development  much  earlier  than  the  Barstow,  Ricardo  and 
Tejon  Hills  faunas. 


1916]   Buwalda:  Miocene  Mammalian  Faunas  from  Tehachapi  Pass     83 

The  horses  of  the  Phillips  Ranch  fauna  appear  more  primitive 
than  those  of  either  the  Mascall  or  the  Virgin  Valley.  They  may  be 
of  a  middle  Miocene  stage,  but  older  than  the  stage  of  either  the 
Mascall  or  the  Virgin  Valley.  The  lower,  or  Phillips  Ranch  horizon, 
appears  to  represent  the  oldest  stage  in  the  development  of  mammalian 
life  above  the  Oligocene  known  thus  far  in  the  region  west  of  the 
Wasatch. 

The  Cache  Peak  fauna  has  been  stated  to  be  more  advanced  than 
that  from  near  Phillips  Ranch.  The  Hypokippus  of  the  Cache  Peak 
assemblage  is  probably  specifically  distinct  from  that  found  at  Bar- 
stow.  The  complete  skull  with  dentition  representing  Merychippus 
differs  somewhat  in  the  details  of  the  facial  region  and  in  its  dentition 
from  Merychippus  calamarius,  a  common  form  at  Barstow,  but  ap- 
pears to  be  quite  near  that  species.  The  Hipparion-like  horse  teeth 
of  the  Cache  Peak  fauna  have  the  protocone  more  distinctly  separated 
than  it  is  in  the  nearest  allied  type  in  the  Barstow  fauna;  this  wide 
separation  is  probably  an  advanced  character.  On  the  other  hand, 
the  Barstow  fauna  contains  horses  which  have  longer  and  heavier  lower 
molars  than  any  found  in  the  Cache  Peak  assemblage. 

The  Dromomeryx  teeth  from  the  Cache  Peak  horizon  seem  consid- 
erably shorter  and  less  advanced  than  the  form  found  at  Barstow. 
The  Merycodus  cannot  be  compared  satisfactorily.  The  Merycochoerus 
form  may  be  different,  but  the  material  is  too  fragmentary  to  permit 
a  certain  comparison. 

Comparing  the  Cache  Peak  with  the  Ricardo,  no  form  is  known  to 
be  common  to  the  two  faunas,  although  the  Merycodus  may  be  the 
same.  The  horses  in  the  lower  part  of  the  Ricardo  section  are  mainly 
very  advanced  types  of  Pliokippus  and  Hipparion. 

The  horses  obtained  in  the  Cache  Peak  horizon  are  all  different 
from  those  so  far  known  from  the  Tejon  Hills,  and  probably  represent 
a  stage  somewhat  older. 

The  Cache  Peak  fauna  is  probably  considerably  older  than  the 
Ricardo,  probably  somewhat  older  than  the  Tejon  Hills,  but  probably 
does  not  differ  greatly  in  age  from  the  Barstow. 

The  Cache  Peak  fauna  represents  a  stage  in  advance  of  that  found 
at  Phillips  Ranch.  The  Cache  Peak  fauna  may  be  late  middle  Miocene 
or  upper  Miocene;  it  may  furnish  a  transition  stage  between  the 
Phillips  Ranch  and  the  Barstow  faunas,  but  it  is  much  nearer  to  the 
Barstow  than  to  the  Phillips  Ranch. 


84  University  of  California  Publications  in  Geology        [VOL.  10 

GEOLOGIC  SIGNIFICANCE  OF  THE  FAUNAS 

The  faunas,  consisting  as  they  do  in  large  part  of  horses,  camels, 
and  antelope-like  forms,  point  to  a  plains  or  open  valley  environment 
in  this  region  in  middle  Miocene  time. 

The  deposits  in  which  the  faunas  occur  are  of  types  which  suggest 
that  they  were  laid  down  under  subaerial  conditions  as  waste  slope  and 
playa  lake  deposits ;  the  evidence  for  this  view  is  corroborated  by  the 
occurrence  of  the  mammalian  remains,  which  are  usually  scattered  and 
frequently  much  gnawed  by  rodents.  The  angularity  of  the  coarser 
terrestrial  deposits  precludes  their  fluviatile  origin,  and  the  lack  of 
classification  and  bedding  in  the  fine  materials  militates  against  their 
being  in  any  large  measure  of  truly  lacustrine  origin.  The  faunas 
and  the  formations  in  which  they  occur  thus  indicate  that  the  climate 
was  one  of  semi-aridity  or  aridity.  Fossil  wood  and  palm  leaves  at 
one  or  more  horizons  probably  do  not  negative  this  view. 

The  age  of  the  faunas  being  established  as  approximately  middle 
and  upper  Miocene  respectively,  stratigraphic  relations  indicate  that 
important  crustal  movements  occurred  in  this  region  between  Jurassic 
and  middle  Miocene  time  and  in  post-middle-Miocene  time. 

The  movements  subsequent  to  the  Jurassic  and  antecedent  to  the 
middle  Miocene  are  indicated  by  the  relation  of  the  mamma] -bearing 
group  to  a  succession  of  sediments  which  lie  with  marked  unconformity 
below  these  strata  and  rest  unconformably  on  the  plutonic  rocks  of 
presumable  Jurassic  age.  This  lower  sedimentary  series,  which  is  well 
exposed  along  lower  Oil  Canon,  has  been  deformed  to  the  extent  that 
the  strata  attain  a  vertical  position  over  much  of  the  area  in  which 
they  are  exposed.  It  is  not  improbable  that  deformative  movements 
affected  the  territory  immediately  previously  to  the  deposition  of  the 
mammal-bearing  group,  inasmuch  as  the  topography  on  w7hich  these 
beds  were  laid  down  was  one  of  some  relief  and  indicates  active  erosion 
immediately  preceding  their  deposition. 

The  crustal  movements  subsequent  to  middle  Miocene  time  in  the 
Tehachapi  Pass  region  are  evidenced  by  the  folding  which  the  mammal- 
bearing  group  has  suffered  since  its  deposition ;  dips  of  twenty  to  thirty 
degrees  are  common  in  the  strata.  Following  this  folding,  erosion 
cut  away  no  small  part  of  the  total  mass  of  the  accumulated  sediments 
and  probably  produced  on  the  region  a  land  surface  of  gentle  relief. 
The  latest  diastrophic  event  was  the  faulting  along  the  southeastern 
base  of  the  present  range,  by  which  the  mountain  area  was  displaced 


1916]   Bmvalda:  Miocene  Mammalian  Faunas  from  Tehachapi  Pass     85 

vertically  2500  to  3000  feet  with  respect  to  the  adjacent  Mojave  Desert 
area.  This  zone  of  displacement  fractured  the  strata  containing  the 
middle  Miocene  mammalian  remains,  so  that  if  there  were  no  other 
basis  for  determining  the  date  of  the  great  displacement  which  gave 
the  southern  Sierra  Nevada  its  present  orographic  features,  the  lower 
limit  in  time  would  be  defined  by  the  upper  Miocene  age  of  the  younger 
of  the  two  faunas.  This  would  indicate  that  the  faulting  occurred  in 
late  Miocene  or  post-Miocene  time.  This  fact  is  of  interest  when  it  is 
recalled  that  some  geologists  have  set  earlier  dates  for  the  faulting  by 
which  the  northern  Sierra  Nevada  attained  its  present  elevation  above 
the  Great  Basin. 

Transmitted  April  9,  1915. 


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